(1) Field of the Invention
The present invention relates to a one-component magnetic developer for use in the electrophotography. More particularly, the present invention relates to a one-component magnetic developer which shows excellent flowability and other developing performances at the development, which prominently improves the image density and image quality of a formed image.
(2) Description of the Related Art
In a one-component magnetic developer, toner particles are frictionally charged with one another and the charged toner particles form a magnetic brush on a developing sleeve having magnets arranged therein, and the magnetic brush is brought into sliding contact with a photosensitive material having an electrostatic image formed thereon to form a toner image. Alternatively, a toner layer is formed on the developing sleeve, and development is carried out under such conditions that vibration or flying of the charged toner is caused between the developing sleeve and the photosensitive material on the surface of the photosensitive material close to the surface of the developing sleeve.
Methods for improving the chargeability and electric characteristics of this one-component developer and further improving the flowability by sprinkling various fine powders on magnetic toner particles have been conducted from old.
For example, the specification of U.S. Pat. No. 3,639,245 teaches that one-component electroconductive magnetic toner particles are sprinkled with gas-phase method silica, and the specification of U.S. Pat. No. 4,082,681 teaches that one-component magnetic toner particles are sprinkled with electroconductive carbon black.
Japanese Unexamined Patent Publication No. 58-1157 teaches that one-component magnetic toner particles or ordinary toner particles are sprinkled with hydrophobic gas-phase method silica together with gas-phase method titania, gas-phase method alumina or hydrophilic gas-phase method silica.
It is considered that these proposals are significant in that the chargeability and flowability of toner particles are improved by incorporating additives of the silica type or the like into toner particles of a one-component magnetic developer. However, in these proposals, only the kind, particles size and amount of the additive are defined. In the state where the developer is practically used, the relation between the toner particles and the additive particles are greatly influenced by the shape and physical properties of the toner particles, but any proposal is not substantially made as regards the toner particles. Moreover, the dispersion state or dispersion structure of the additive on the surfaces of toner particles are not referred to.